1. Technical Field
This invention relates generally to transformers and in particular to auto-transformers for phase shifting. Still more particularly, the present invention relates to auto-transformer for use with multiple pulse rectifiers.
2. Description of the Related Art
The operation, design, and functionality of basic auto-transformers are generally known in the art. For example, it is well known in the art that auto transformers can transform electric energy using less mass of conductor and core than equivalent isolation transformers.
One major limitation with auto-transformers is that they typically do not block the flow of unwanted, zero sequence currents, particularly when the auto-transformers are utilized with multiple pulse rectifier applications. With conventional auto-transformers, blocking these unwanted zero sequence currents requires the utilization of additional components, such as inter-phase transformers or zero sequence blocking transformers. These additional components necessarily add to the overall cost of the system. The above limitation of auto-transformers is clearly described in Power Electronic Converter Harmonics authored by Derek Paice (I.E.E.E., 1999).
Clearly, the industry would receive a significant benefit if an auto-transformer was designed that was not burdened with the above limitations and that did not require utilization of additional components for blocking these zero sequence currents.